The invention relates to a connection establishment method comprising a random access type connection establishment using a random access channel, which is used in a radio system comprising several subscriber terminal equipments and base stations where one or more transceiver units operate, and in which system the connection establishment between the subscriber terminal equipment and the base station is possible when the subscriber terminal equipment is situated in the coverage area of one or more transceiver units of the base station, in which area the subscriber terminal equipment evaluates the quality of the connections to be established.
The invention further relates to a subscriber terminal equipment which is arranged to establish a random access type connection by using a random access channel in a radio system comprising several subscriber terminal equipments and base stations which comprise one or more transceiver units, and in which system the connection between the subscriber terminal equipment and the base station is possible when the subscriber terminal equipment is situated in the coverage area of one or more base station transceiver units, where the subscriber terminal equipment comprises an evaluation means for monitoring the quality of the connections to be established.
The invention also relates to a radio system comprising several subscriber terminal equipments and base stations which comprise one or more transceiver units and where the subscriber terminal equipment is arranged to send a random access type connection establishment request via a random access channel and in which system the connection between the subscriber terminal equipment and the base station is possible when the subscriber terminal equipment is situated in the coverage area of one more transceiver units of the base station, in which area the subscriber terminal equipment comprises an evaluation means for monitoring the quality of the connections to be established.
A typical cellular radio system, such as the CDMA system (Code Division Multiple Access), comprises a set of subscriber terminal equipments and base stations. When a subscriber terminal equipment has no connection on a normal traffic channel, it monitors paging channels of the base station and when necessary, sends messages on an access channel to the base station. The paging channel and the access channel provide an organization channel. When a connection is established in the cellular radio system between a subscriber terminal equipment and a base station, either the subscriber terminal equipment or the base station sends a connection establishment request on the organization channel. A specific Random Access Channel (RACH), which is a channel of a subscriber terminal equipment is typically used as an access channel in the CDMA cellular radio system for establishing a connection from among all the possible access channels and from among the phases available for the phase of a pseudo-noise code. When a radio connection is to be established, the terminal equipments send a connection establishment message via an access channel to the base station which forwards it to the system where traffic channel resources are allocated to the connection. When the base station requests a traffic channel connection, it sends via a paging channel a request to the subscriber terminal equipment which responses to the paging by requesting a traffic channel for its use via the access channel.
In the CDMA system, each base station sends continuously a pilot signal so that there is a specific pilot signal in different sectors or beams of the base station because each sector and beam has a specific base station transceiver unit. It is previously known to use a pilot signal for identifying a base station, a beam or sector of the base station. A pilot signal is a spread-coded signal without data modulation which signal each base station sends continuously to its coverage area. The terminal equipment may identify the base station transceiver units by the pilot signal because the phases of the spreading codes in the pilot signal differ from one another. The subscriber terminal equipments continuously carry out measurings of pilot signals, and subscriber terminal equipments establish an active group of the base station transceiver units providing the best connections, the base station transceiver units in the group being utilized when establishing new connections.
Each base station also sends on a sync channel. A signal of the sync channel may be demodulated and detected whenever the pilot signal can be identified. Information is transmitted on the sync channel about the base station, about the power and the phase of the pilot signal and about the size of uplink interferences.
In addition to a circuit-switched connection, the base station and the subscriber terminal equipment may communicate over a packet-mode connection which is used in the PRMA system (Packet Reservation Multiple Access). In that case the channel needed for transmitting the signal is only reserved for the duration of the signal and it is released immediately when the signal is discontinuous or when it ends or has a break. If the signal is sent discontinuously, the channel has to reserved again after each break.
In prior art solutions, when a subscriber terminal is establishing a connection with a base station on the access channel, the connection is only to one base station, sector or beam of the base station. Access channel and paging channel connections are used especially when establishing a traffic channel connection, in which case when the connection establishment is successful, the traffic channel will, at least at first, have a connection to only one base station, sector or beam of the base station. This raises a need to increase considerably the transmission power of the subscriber terminal equipment and/or the base station and carry out fast an updating of the active group, whereby interference level and the amount of signalling will increase. Furthermore, during a packet-mode transmission it is difficult to carry out soft handover in the middle of the packet although the quality of the connection during the transmission would change to be favourable for handover.
The object of the present invention is to accomplish a solution which will diminish interferences relating especially to the initial stage of the connection and enable the use of macrodiversity also for a packet-mode connection.
This is achieved with a method as shown in the preamble which is characterized in that the subscriber terminal equipment forms a random access type connection to more than one base station transceiver unit included in one or more base stations.
The subscriber terminal equipment of the invention is characterized in that the subscriber terminal equipment comprises a control means for controlling a random access type connection establishment to more than one base station transceiver included in one or more base stations.
The radio system of the invention is characterized in that the radio system comprises subscriber terminal equipment which is arranged to control a random access type connection establishment between the base station and the subscriber terminal equipment so that it is possible for the subscriber terminal equipment to establish a connection to more than one base station transceiver unit included in one or more base stations.
Considerable advantages are attained with the solution of the invention. By using the method of the invention, macrodiversity state will be assumed from the beginning of connection establishment. In that case the updating of the active group is required less and at the beginning of the connection, a lower transmission power can be used than in prior art solutions. In this way the need for signalling will be reduced and the capacity of the system will increase.
In a packet-mode data transmission, macrodiversity state will also be assumed directly, the state continuing for the duration of the whole packet in which case the quality of the provided connection will worsen less probably during the packet. The use of macrodiversity on a packet-mode connection is possible only by a method according to the invention because it is difficult to carry out soft handover during a packet.
In the SDMA technique (Space Division Multiple Access) the transmission and reception of the base station takes place in narrow beams, each of which has a specific base station transceiver unit. In that case the best connection is enabled with the method of the invention.
The preferred embodiments of the method of the invention will also appear from the appended dependent claims, the preferred embodiments of the subscriber terminal equipment of the invention will appear from the appended dependent claims relating to the subscriber terminal equipment and the preferred embodiments of the radio system of the invention will appear from the appended dependent claims relating to the radio system.